This invention pertains to compact and lightweight turbine propulsion systems with improved part load fuel consumption. Most turbine users would prefer the simple Brayton cycle engine (Jet Aircraft Power Systems by Casamassa and Bent, McGraw-Hill Book Company, 1957 discusses the Brayton cycle). In the 2000 to 5000 SHP Class it is possible to obtain a specific fuel consumption of 0.42 lb/hr/SHP at maximum power using a Brayton cycle turbine. This performance has been achieved with a pressure ratio at the compressor of 16 to 1 and a cycle temperature of 2200 degrees F. Under partial load conditions, however, this same engine burns more fuel per unit of output. At 50 percent load, the specific fuel consumption may increase to 0.5 lb/hr/SHP.
One means of improving fuel efficiency under part load conditions is to use a regenerative cycle engine. U.S. Pat. No. 3,222,864 to Dyste et al. is an example of such an engine. The regenerative gas turbine engine includes a waste heat recovery device which preheats the inlet air as it leaves the compressor, using the heat from the turbine exhaust gases.
The U.S. Pat. No. 3,011,311 to Williams et al. discloses another approach for using a heat exchanger for improving fuel economy. U.S. Pat. No. 3,032,989 to Oprecht is another example of a gas turbine operating on the regenerative principle. U.S. Pat. No. 3,302,397 to Davidovic shows how a heat exchanger can be used to cool critical components within a turbine engine.
Regarding heat exchangers adapted for use on turbine engines, there are many examples in the literature. The following U.S. Pat. Nos. exemplify the art: 3,143,166 to Williams et al.; 3,222,864 to Dyste et al.; 3,228,464 to Stein et al.; 3,424,240 to Stein et al.; 3,785,435 to Stein et al; 3,831,674 to Stein et al.; and, 4,008,569 to Bennett.
With regenerative turbine engines the lowest specific fuel consumption can be moved to the 40 to 60 percent of maximum power range. In the past, most turbine users have tended to avoid the regenerative system in favor of the simpler Brayton cycle engine. However, with the increase in fuel costs, the use of a regenerator becomes more cost effective.
Multiple cycle turbine installations have long been used in large power plants where horsepower to weight ratios are not critical. U.S. Pat. No. 2,654,217 to Rettaliata is an example of a gas turbine system embodying a high pressure turbine and a low pressure turbine operating cooperatively to obtain optimum efficiency for part load conditions.
None of the above provide the features of my dual cycle turbine system. Using a combination of two engines with different pressure ratios and a cross connected common regenerator, I obtain low specific fuel consumption at both full and part load while at the same time have an engine system with a maximum output of about 4 HP per pound of engine weight.